The disclosures herein relate generally to computers and more particularly to an apparatus for reducing electromagnetic emissions from a computer.
The operating frequencies of system components in electronic devices such as computers are continually increasing. As the operating frequency increases, the wavelength of electromagnetic emissions from the system component decreases. The reduced wavelength enables electromagnetic emissions to escape through discontinuities that are too small to be breached by emissions having a larger wavelength. As a result, the performance of many previous apparatus and methods for controlling electromagnetic emissions in an electronic device are rendered inadequate in electronic devices having system components running at relatively high operating speeds.
RAMBUS In-Line Memory Modules, also referred to as RIMM modules, illustrate one example of high performance system components that operate at a relatively high operating speed. The performance of RIMM modules is attained through a high-speed bus enabling clock speeds in excess of 400 MHz. Through the use of one or more riser cards, RIMM modules may be configured to provide memory in excess of 8 GigaBytes.
A riser card is connected to a memory connector on a motherboard of the computer and a plurality of RIMM modules are connected to the riser card through corresponding RIMM connectors that are mounted on the riser card. In this configuration, the RIMM modules are in elevated, parallel relationship with respect to the motherboard. The quantity of RIMM modules and their orientation above the motherboard in open space results in increased electromagnetic emissions and complicates the task of containing these emissions within the computer.
When designing a computer system using RIMM modules, as well as other types of heat generating system components, it must be taken into consideration that the performance and operating life of these types of system components are adversely affected by excessive temperatures. The magnitude of memory attainable with RIMM modules and the frequency at which RIMM modules operate can result in the generation of tremendous quantities of heat. As a result, it is necessary to use a apparatus to control the operating temperature of these types of heat generating system components.
U.S. Pat. No. 5,731,633 discloses a semiconductor module such as a memory module. The semiconductor module includes a composite substrate comprising a printed circuit substrate with a thin metal cover laminated to a first side of the printed circuit substrate. A plurality of semiconductor devices such as memory chips are mounted to a second side of the printed circuit substrate. The semiconductor module is configured to be mated with a connector mounted on a main printed circuit board in a computer such as a motherboard, or with a connector mounted on an expansion card.
U.S. Pat. No. 5,519,585 discloses an electromagnetic emissions shield that is removably secured to a side of a printed circuit substrate. The shield includes a polymeric layer with a metallic conductive layer formed on the polymeric layer. The portion of the overall strength of a system component that is attributed to shielding is negligible and the inherent strength of the shield is minimal with regard to the total required strength of a system component. Furthermore, the shield does not substantially aid in mounting the system component to a corresponding electronic device.
U.S. Pat. No. 4,872,212 discloses an electronic device which includes a plurality of electromagnetically isolated modular units. The modular units are interchangeably and detachably mounted in an electromagnetic containment enclosure. The enclosure includes a plurality of sides and an open face. Each modular unit includes a shielding member and a system component mounted on the shielding member. Each shielding member includes an edge member. A plurality of modular units may be stacked in the enclosure such that the edge members form a segmented wall in the opening for limiting the escape of electromagnetic emissions from the opening.
Electromagnetic emissions become problematic when they encounter a non-shielded portion of an electronic device such as a gap between two panels of a metal chassis or an opening formed in a face of the chassis. Provided that the wavelength of the electromagnetic emission is smaller than a corresponding dimension of the unshielded portion of the electronic device, the emissions may breach the confines of the enclosure of the electronic device. These emissions may similarly breach and enter the enclosure of adjacent electronic equipment, potentially causing electromagnetic interference (EMI) with respect to the operation of the adjacent electronic equipment. To limit the potential for adverse operation of equipment resulting from EMI, regulation agencies such as the Federal Communications Commission (FCC) have imposed limits on the allowable levels of electromagnetic emissions emitted from many electronic devices, including computers.
Accordingly, there is a need for an apparatus that provides improved containment of electromagnetic emissions from system components running at relatively high operating frequencies in an electronic device while allowing the system components to be mounted for permitting enhanced cooling of the system components.